Character Rigging - Game Character Development with Maya - page 708

FIGURE 12.6 Example of forward kinematics (FK)
AnimatingwithFKishighlyrecommendedbecauseinmanycasesitproducesbetter,more
naturallookingmovements—butit'snotalwayspractical.Saythecharacterisleaningwith
a hand on a table; we would need the hand to stay locked while the character's upper body
moves. Keeping the hand steady using FK would be practically impossible, but with in-
verse kinematics it's a piece of cake.
Inverse kinematics works opposite to FK. As suggested by its name, in IK the joint chain
is evaluated backward . Figure 12.7 , left, shows the hand on the table with an IK handle
applied (the cross located at the wrist). The IK handle dictates the position of the wrist,
lockingitinplace.Therestofthearmthenfollows.Ifwemovethemainjointsofthebody
forward ( Figure 12.7 , right), you can see that the wrist stays where it is. The hand remains
locked, resting on the table, because the IK handle is not parented to (controlled by) any
joints in the skeleton. The shoulder and elbow joint rotations are calculated by the IK solv-
er (explained shortly) to allow for the best possible position and orientation of the skeleton
chain between the shoulder and the wrist.
FIGURE 12.7 Example of inverse kinematics (IK)
IK Solvers
IK solvers are the brains behind IK handles. They work out how to rotate each joint in a
joint chain controlled by an IK handle. There are three types of IK solvers in Maya: IK
Single Chain solver, IK Rotate Plane solver, and IK Spline solver.